Document HostServices() as the per-instance block-pool escape hatch, and the instance-pool sizing decision from the symposium port: pool=4 / 512 MiB per instance validated against the 45 MiB symposium module (p50 5.5ms / p95 9.4ms per 3-block page; ~628 MiB RSS at pool=4, fits the 4 GiB container default). Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>